1. Field of the Invention
This invention relates to an X-ray fluorescence spectrometer using a beam-collimating method and, more particularly, to an X-ray fluorescence spectrometer suited for local analyses of a specimen.
2. Description of Related Art
As shown in FIG. 10, an X-ray fluorescence spectrometer using a beam-collimating method contains a specimen 2 inside a specimen container 8. Only a selected portion of the surface of the specimen 2 at the center of the container 8 is exposed to the exterior of the container 8 for local analyses. As the primary X-rays from an X-ray tube 1 irradiate the specimen 2 thus disposed, fluorescent X-rays are generated at a local portion of the specimen 2 and are guided through a view-restricting screen 3 to primary Soller slits 4. The Soller slits 4 serve to collimate the fluorescent X-rays and to guide them to an analyzing plate crystal 5, which disperses the incident fluorescent X-rays into a spectrum of different wavelengths corresponding to the elements contained in the specimen 2. The dispersed beam is thereafter led to secondary Soller slits 6, collimated thereby and received by an X-ray detector 7 for detecting the elements in the local portion of the specimen 2 from the detected spectrum.
With an arrangement as described above, it is difficult to have only the specimen 2 irradiated with the primary X-rays from the X-ray tube 1 because a part of the primary X-rays is likely to irradiate the container 8. As a result, the irradiation by the primary X-rays may cause not only the generation of fluorescent X-rays from the local portion intended to be analyzed, but also the generation of fluorescent and scattered X-rays from the container 8. If such fluorescent and scattered X-rays from the container 8 are additionally received by the X-ray detector 7 through the Soller slits 4 and 6 as described above, they create a background against the spectrum of the fluorescent X-rays of interest for the analysis of the elements in the local portion of the specimen 2. In other words, the signal-to-noise ratio (S/N) of the X-ray detector 7 is adversely affected. This is why the view-restricting screen 3 is interposed between the specimen 2 and the primary Soller slits 4 to limit the field of view from the primary Soller slits 4 to the local portion of the specimen 2.
As shown more clearly in FIG. 11, the specimen 2 is retained in the container 8 with its peripheral portion covered such that only its local portion at the center is externally exposed. The view-restricting screen 3 is composed of a flat plate 3a having a plurality of holes (such as three holes 3b, 3c and 3d) each corresponding to the size of different one of the local portions to be analyzed. In situations where local portions with different sizes are to be analyzed, the screen 3 is slid in the direction indicated by an arrow A such that a hole of an appropriate size will be positioned at the center of the container 8.
If the local portions to be analyzed are at different positions but are of the same size, the screen 3 need not be moved, but the specimen 2 is moved from one position to another such that each local portion to be analyzed will come to the center position of the container 8. Depending on the shape and/or size of the specimen 2 with respect to the container 8, however, it may be difficult to place certain local portions precisely at the center as required. In such a situation, it may be necessary to subdivide the specimen 2 into smaller parts. It now goes without saying that such a process makes the analysis very troublesome.
When the exposed area of the specimen 2 is increased, or when the local portions to be analyzed are large, the distance by which the specimen 2 or the container 8 must be moved becomes also large. Depending on how various internal components of the spectrometer, such as the X-ray tube 1, are arranged, there may not be enough room to move the container 8 as required. If it is attempted to secure enough space for maneuvering the container 8, this may have an adverse effect on the detection sensitivity of the X-ray detector 7.